For us UNIX fans, Sun Microsystems is working with Amazon to offer OpenSolaris on EC2.
I’m not sure how I missed it, but they made the announcement last week.

I just signed up to be included in the beta. I’ll post an update here when I get in and start tinkering. My main focus is going to be the performance of MySQL on EC2 comparing Linux with OpenSolaris.

I’m not sure what their long term plans are, but for now they aren’t incurring any extra charges (beyond the standard EC2 charges.) I know that RedHat charges extra to run their Enterprise version on EC2.